This invention relates to seismic exploration of water-covered areas of the earth where long seismic cables are used to detect seismic energy produced near the end of the cable.
In the past these long seismic cables normally have contained detectors grouped into a number of equal length arrays throughout the cable. In some special applications seismic cables having relatively short arrays of detectors have been used near the end of the cable at which the seismic energy source is located and longer arrays have been used farther from the source. The close-in seismic arrays of detectors were used to delineate shallow subsurface formations while the longer arrays were used to delineate moderate to deep reflecting horizons. However, this procedure discriminates against the higher frequency seismic energy which penetrates the earth to considerable depths that is useful for more exactly delineating subsurface earth formations. This procedure also discriminates against seismic energy arriving at the array at large angles off the vertical. With the advent of nondynamite seismic sources capable of generating appreciable seismic energy at higher frequencies, i.e., 50 to 1000 Hz, conventional seismic cables have been found to produce records which are so badly distorted as to be unusable in many instances.